Well intervention operations on subsea wells have contributed to considerable increases in production. When a subsea well is in drilling mode, the necessary equipment includes a blowout preventor (BOP) stack, a disconnectable lower marine riser package and a marine riser portion. For well intervention through a subsea christmas tree, a different pressure control system is used comprising a safety package to contain the well, a disconnectable riser portion and a dual string workover riser system. One string communicates with the production tubing, while the other string communicates with the tubing annulus. These well intervention systems require complex and expensive handling and running systems that occupy a large amount of space on floating vessels. Such large systems may cause problems including limiting storage of other equipment.
Dual-string skeletal workover risers are used in two roles. One role is within the marine riser to run and retrieve a well completion tree. Second, dual-string skeletal workover risers are used to deploy the Christmas tree and intervention equipment in open water. In both cases, the equipment provides well control functions required in a well intervention role.
With a marine riser, the through riser equipment is not subjected to open-water environmental loads. Consequently, the equipment is not required to offer the structural integrity to resist the bending and tensile forces experienced in an open-water environment. However, the equipment does provide the well control functions required in a well intervention role.
It is desirable to create a system that offers all the functions of both a through-BOP and open-water system, but that provides a lightweight intervention role, i.e. one without a BOP stack, which was previously unavailable or impossible with existing systems.
Such a system may be achieved by providing a lightweight intervention system for use with single-bore and dual-bore intervention operations, which can be used with both horizontal trees, conventional trees and with wellheads without trees mounted thereon.